We investigate palm species distribution, richness and abundance along the Mokoti, a seasonally-dry river of southeastern Amazon and compare it to the patterns observed at a large scale, comprising the entire Brazilian territory. A total of 694 palms belonging to 10 species were sampled at the Mokoti River basin. Although the species showed diverse distribution patterns, we found that local palm abundance, richness and tree basal area were significantly higher from the hills to the bottomlands of the study region, revealing a positive association of these measures with moisture. The analyses at the larger spatial scale also showed a strong influence of vapor pressure (a measure of moisture content of the air, in turn modulated by temperature) and seasonality in temperature: the richest regions were those where temperature and humidity were simultaneously high, and which also presented a lower degree of seasonality in temperature. These results indicate that the distribution of palms seems to be strongly associated with climatic variables, supporting the idea that, by 'putting all the eggs in one basket' (a consequence of survival depending on the preservation of a single irreplaceable bud), palms have become vulnerable to extreme environmental conditions. Hence, their distribution is concentrated in those tropical and sub-tropical regions with constant conditions of (mild to high) temperature and moisture all year round. KEY-WORDSAmazon, diversity, moisture, palms, tropical forests. Determinantes meta-espaciais da distribuição de palmeiras RESUMO Investigamos a distribuição, riqueza e abundância de espécies de palmeiras ao longo do Rio

The hypothesis that forest disturbance is important for the recruitment of the large arborescent palms Attalea maripa was tested with a natural experiment in the Pinkaití site (7 o 46'S; 51 o 57'W), a seasonally-dry Amazonian forest. A 8,000 m long trail, that crosses, in its lower half, an open forest along the Pinkaití stream bottomlands and, on its upper half, a dense forest on a hill, was divided in 160 0.15 ha (50x30 m) sampling units. At each unit, adult palms were counted and percentage of canopy openness was measured with a concave spherical densiometer. The palms were nearly five times more abundant at the bottomlands, whose forest had a canopy 14.8% more open than that of the hill; supporting the hypothesis that disturbance is important for their recruitment. Key words: Attalea maripa, Forest dynamics, Palm trees, Forest regeneration ResumoA hipótese de que a perturbação florestal é importante para o recrutamento da palmeira arborescente de grande porte Attalea maripa foi testada com um experimento natural na base de pesquisas do Pinkaití (7 o 46'S; 51 o 57'W), uma floresta Amazônica sazonalmente seca. Uma trilha de 8.000 m de comprimento que cruza, em sua metade baixa, uma floresta aberta ao longo da baixada do rio Pinkaití e, em sua metade alta, uma floresta densa em uma serra, foi dividida em 160 unidades amostrais de 0,15 ha (50x30 m). Em cada unidade, palmeiras adultas foram contadas e a percentagem de abertura do dossel foi medida com um densiômetro hemisférico côncavo. As palmeiras foram quase cinco vezes mais abundantes na baixada, cuja floresta teve um dossel 14,8% mais aberto que aquele da serra, apoiando a hipótese de que perturbação é importante para seu recrutamento. Palavras-chave: Attalea maripa, Dinâmica florestal, Palmeiras arborescentes, Regeneração florestalBiota Neotropica v5 (n1) -http://www.biotaneotropica.org.br/v5n1/pt/abstract?article+BN00305012005

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This study investigates patterns of forest structure and tree species diversity in an anthropogenic palm grove and undisturbed areas at the seasonally-dry Pinkaití research station, in the Kayapó Indigenous Area. This site, managed by the Conservation International do Brasil, is the most southeastern site floristically surveyed in the Amazon until now. The secondary and a nearby undisturbed forest were sampled in a group of 52 floristic plots of 0.0625-ha (25x25-m) where all trees with DBH $ 10 cm were measured and identified. The analyses were complemented with other two floristic plots of 1-ha (10x1000-m). The present study has shown that the Pinkaití, like other seasonally-dry forests, have great heterogeneity in forest structure and composition, associated with biotic characteristics of the most important tree species, natural disturbance and history of land-use. The palm grove, moderately dominated by the arborescent palm Attalea maripa (Aubl.) Mart., presented high tree species diversity and was floristically similar to undisturbed forests at the study site. It is discussed the importance of large arborescent palms for the seasonally-dry Amazon forests regeneration. KEY WORDSAmazon, anthropogenic forest, arborescent palms, floristics, tropical forests. PALAVRAS-CHAVEAmazônia, florística, floresta antropogênica, floresta tropical, palmeiras arborescentes.

In this study we propose a model that represents the importance of large arborescent palms in the dynamics of seasonally-dry Amazonian forests. Specifically, the model is aimed at guiding the investigation of the role of large arborescent palms on forest regeneration and succession. Following disturbance, the high level of luminosity reaching recently formed forest gaps favors the quick proliferation of shade-intolerant lianas that, by casting shade on the crowns of mature forest trees and increasing tree-fall probability, suppress forest succession. Due to their columnar architecture palm trees are, however, not severely affected by vines. As the palms grow, the canopy at the gaps becomes gradually higher and denser, progressively obstructing the passage of light, thus hindering the growth of shade-intolerant lianas and enabling late-successional tree development and forest regeneration. Owing to the long time associated with forest regeneration, the model cannot be tested directly, but aspects of it were examined with field data collected at an Attalea maripa-rich secondary forest patch within a matrix of well-preserved seasonally-dry forest in the Southeastern Amazon. The results indicate that (1) forest disturbance is important for the recruitment of large arborescent palms species, (2) these palms can grow rapidly after an event of disturbance, restoring forest canopy height and density, and (3) secondary forest dominated by palm trees species may be floristically similar to nearby undisturbed forests, supporting the hypothesis that the former has undergone regeneration, as purported in the model. Key words: Amazon, Attalea maripa, forest dynamics, palm trees, regeneration. ResumoNeste estudo propomos um modelo que representa a importância de palmeiras arborescentes de grande porte na dinâmica das florestas amazônicas sazonalmente secas. Especificamente, o modelo visa guiar a investigação do papel destas palmeiras na regeneração da floresta. Após um evento de perturbação, a alta luminosidade das clareiras recentes favorece a rápida proliferação de lianas dependentes de insolação que, sombreando as copas das árvores e aumentando sua probabilidade de queda, tendem a interromper o processo de sucessão. Devido a sua arquitetura colunar, as palmeiras arborescentes, no entanto, não são severamente afetadas por lianas. À medida que estas palmeiras crescem, o dossel das clareiras se torna gradualmente mais alto e denso, limitando desta forma o crescimento das lianas e permitindo o desenvolvimento das árvores de estádios sucessionais tardios e, consequentemente, a regeneração da floresta. Devido ao longo período associado à regeneração da floresta o modelo não pode ser testado diretamente, mas aspectos deste foram examinados com dados de campo coletados em uma mancha de floresta secundária rica em Attalea maripa em uma matriz de florestas primárias bem preservadas no sudeste da Amazônia. Os resultados revelam que (1) eventos de perturbação florestal são importantes para o recrutamento das palmeiras arboresce...